Intentional damage would carry a maximum penalty of 12 months' imprisonment, or a fine of up to $50,000 for an individual or $100,000 for a group.

Seismic vessels would also be able to keep protesters up to 500 metres away, and those in violation would be fined $10,000.

Mr Bridges says offshore protests by Greenpeace against Petrobras in 2011 is one of the main reasons for the law change.

At the time, Greenpeace deployed swimmers in front of the Brazilian oil giant's survey ship in the waters off the North Island's East Cape.

Mr Bridges says the proposed legislation is not about thwarting legitimate democratic protest - but stopping dangerous and reckless behaviour.

"What we are doing here is stopping people who want to stop other people going about their lawful business and doing what they have a permit to do and they are legally entitled to do."

Mr Bridges says while there is protection for oil rigs from unlawful damage in New Zealand's exclusive economic zone, there is none for vessels or other moveable structures, and the new law would fill that gap.

Greenpeace says Govt using scare tactics

Greenpeace says the Government is using scare tactics with its new proposal to fine anti-mining protesters who interfere with offshore mining operations.

It says the law is going to stop the same sort of people who would have protested against nuclear testing in the Pacific and nuclear warships entering New Zealand waters.

The Labour Party says the proposed fines are a massive over-reaction and the Government is kow-towing to foreign multi-national companies.

But Mr Bridges says companies who have gone through a legitimate permit process deserve to carry out their work free of criminal interference.